Worldwide oil and gas development has shifted from conventional reservoirs to unconventional and deepwater reservoirs, characterized by high pressure, high temperature, ultra-low permeability, and extensively developed natural fractures. This transition to increasingly hostile environments introduces new challenges in well drilling and completion, such as downhole drilling issues, formation damage, and reduced productivity. Aiming to solve the challenges, drilling and completion technologies have excelled greatly in the past two decades. This book covers managed pressure drilling (MPD), the role of artificial intelligence (AI) in refining drilling processes, and the transformative effects of digitalization and automation. Emphasizing efficiency, safety, and environmental responsibility, the book also integrates methods like casing while drilling for improved efficiency, advanced diagnostics for rig safety, stabilization techniques for wellbores in fractured reservoirs, cement sheath integrity maintenance, and the optimization of continuous gas lift. Bridging theoretical concepts with practical applications, the narrative offers insights into both operational techniques and safety strategies, drawing from past experiences. The current state-of-the-art theories, technologies, and practices are covered, bridging the gaps between fundamental theories and engineering applications.